1. Field of the Invention
The invention relates to a method for network regulation upon threshold value overshoots in a low voltage or medium voltage network, where control commands are transmitted from a central regulation unit of the low voltage or medium voltage network to controllable components of the low voltage or medium voltage network. The invention can be used respectively for just a low voltage network or just a medium voltage network.
2. Description of the Related Art
Low voltage networks are part of the power network for distribution of the electrical energy to the majority of the electrical consumers, which consists of low voltage devices. In order to prevent voltage losses, low voltage networks are restricted in their spatial extent to a region from a few 100 m to a few kilometers. They are therefore fed regionally by transformer stations from a higher-order medium voltage network. In Europe, they are typically operated at a network voltage of 230 V (between each phase conductor and the neutral conductor) or 400 V (between the three phase conductors), and in any event only up to 1000 V. The rated power output of individual distribution transformers can vary according to the target system planning of the respective distribution network operator, but typically lie in the range of 250 or 400 kVA for rural areas and 630 or 800 kVA for inner city areas.
The expression “low voltage network” in the sense of this invention refers to a part of the distributor network, i.e., a portion that is supplied with electrical energy by a particular distribution transformer.
Components of the low voltage network can be: electrical generators (e.g., photovoltaic systems, or small wind generator systems), storage units (e.g., batteries, heat pumps, or charging stations for electric vehicles), flexible consumers (e.g., electric storage heaters, buildings with and without building automation system) and network operating equipment (e.g., transformers, transmission lines, fuses, or measuring devices such as Smart Meters).
Herein, particularly electrical generators, storage units and flexible consumers can be configured as controllable components.
Medium voltage networks are part of the power network for distributing the electrical energy over distances in the range of a few kilometers to 100 km in rural areas. Medium voltage networks are typically operated at a maximum voltage of between 1 kV and 52 kV, in particular at 10 kV, 20 kV or 30 kV. A medium voltage network typically serves for electrical energy supply to a region that comprises a plurality of villages or, in cities, an urban district. Medium voltage networks of the regional distribution network operators are typically fed in transformer substations from the higher-level high voltage network, such as the 110 kV level (distribution network level), and serve to feed the regionally distributed transformer stations that supply the individual low voltage networks to the end customers. Larger power consumers, such as industrial plants and hospitals, but also large swimming baths and major transmitting towers, usually have their own medium voltage connections with their own substations.
The power transformers needed for the supply lie in the range from 20 MVA to 60 MVA. Typically, these power transformers are also the last level at which load-dependent voltage variations can be compensated for by stepping switches. If needed, for large feed power levels from decentrally obtained regenerative energy sources, electronic medium voltage regulators can be used.
Medium voltage networks are implemented in their topology as radial systems or as ring systems and, particularly in urban regions, ring feeders are common. Medium voltage networks can be fed from a plurality of points and smaller generating plants such as wind generator systems, biogas systems and large photovoltaic systems feed into regional medium voltage networks.
In a medium voltage network, in particular, power transformers, medium voltage regulators, electrical generators, storage units and flexible consumers can be configured as controllable components.
The classic power supply operation for electrical supply is facing great challenges due to the increasing establishment of decentralized, mostly renewable, energy generating plants (DEA, typically in the power range from 3 to 100 kW). Added to this is the development of electric vehicles and therefore an increased substitution of other energy transmission forms by electricity. Due to the change of the energy system from one based on conventional energy sources to one based on renewable energy sources, the need for flexibility is growing. This arises from the fact that many renewable energy sources (wind, solar, water) are available only depending on the situation and not according to pre-determined timetables. Thus, the former principle of “generation following consumption”, has to undergo a fundamental change to “consumption following generation”.
“Flexibility providers” are tools for adapting use to generation. A flexibility provider is to be regarded as a large group of different uses. In the simplest case, this can be flexible loads, e.g., heat pumps, charging points for electric vehicles, circulating pumps, electric heating systems, electric boilers that are reduced or switched off. On the generating side, the feed-in of renewable or conventional generating plants (wind power plants, photovoltaic plants, power/heat coupling systems) could be reduced. If an electrical storage unit is also available, possibly even in combination with flexible loads or generating plants, flexibility is possible in all power directions.
The core question of the energy revolution seen on an industrial scale is how the individual network participants (only or additionally) consuming energy, for example, buildings or groups of buildings, can participate with as little influence on them as possible in different energy markets in order to develop, for example, the city as a source of flexibility to support the integration of renewable energy sources. Herein, it must be ensured that the permissible limit values (voltage, maximum power, frequency) in the energy supply network, for example, in the low voltage network, are not breached.
Network bottlenecks can arise because the participation in energy markets and the use of internal storage units (which are not recognizable from the network viewpoint because they are located, for example, within buildings or industrial sites) can alter the previous temporal distribution of the load (e.g., according to the standard load profile H0). Many prosumers (customers who produce and consume energy) receive the same information concerning inexpensive energy and change their usage behavior accordingly. The conventional assumptions regarding simultaneity are no longer valid and severe load spikes can arise. If these load spikes breach the limit values of the energy supply network, intervention is necessary.
The “smart grid” is regarded as a solution to these problems. The smart grid or intelligent power network comprises the communicative networking and control of electrical generators, storage units, electrical consumers and network operating equipment in energy transmission and energy distribution networks of the electricity supply system.
In future, “smart buildings”, also known as intelligent houses or intelligent buildings, will also contain components such as fluctuating generators (e.g. photovoltaic systems, small wind generator systems), flexible consumers and storage units for electrical energy, or, for example, the charging infrastructure for electric vehicles. The building is made “smart” or intelligent by the use of a modern building automation system (CEMS—consumer energy management system). Building automation comprises the totality of monitoring, control, regulation and optimization equipment in buildings. It is an aim to carry out functional sequences across all components independently (automatically) and according to pre-determined setting values (parameters). All sensors, actuators, operating elements, consumers and other technical units in the building are networked together. Sequences can be grouped together in scenarios. A characterizing feature is the networking throughout via a bus system.
The building automation systems of smart buildings and/or the energy management systems as part of the building automation systems must therefore optimize the energy requirement for electrical and thermal energy for the individual components of the building, create local (related to the building) prognoses and take account of flexible tariff information that contains market and/or network-specific portions.
A low voltage network comprises different active components that cooperate in the low voltage network. There is a plurality of types of consumers, generators and mixed forms. The connected buildings can have no remotely readable meters, be equipped with “smart meters” or can be equipped with a building management system. In addition, there is the distribution network operator who operates a, where possible regulable, distribution transformer (RONT) and thus operates the existing low voltage network. Together, all these components form the local branch circuit in which the network constraints must be adhered to.
None of the components mentioned above can remedy any network problems without throttling. Conventionally, for example, inverters were equipped with a P/Q infeed limitation (e.g. voltage-dependent effective power characteristic curves and reactive power characteristic curves), which prevents too much power from being fed into the low voltage network in the event of a local threshold value overshoot. Thus, although adherence to the network constraints is ensured locally, it not certain that either the throttling of these components is sufficient, or that throttling is not too severe and that thereby less energy than possible is obtained.
An attempt to disentangle the market overview and the network overview is the “network traffic lights”. The states red, amber and green reflect the respective network states. The individual components, in particular the generators can only operate in the green state where, from the local network viewpoint, no limitations exist and all the market mechanisms (e.g., making system services available for transmission networks) can be used without restriction or, in the red state, where the network constraints require strict stipulations for feed-in and thus market mechanisms are locally restricted for a limited time. In the amber state, overloading is to be expected and, within the network constraints, a market-based optimization of the capacity utilization of the low voltage network can be undertaken, that is, an optimization of the energy supplied by the individual components (e.g., the generators in the low voltage network) or to energy supplied to the individual market participants with regard to the prevailing applicable energy price. Herein, more or less complex mechanisms that are aimed at enabling as many market requirements as possible without severe restriction are considered.
In the red region, the distribution network operator (network operator for short) is enabled to protect his distribution network. Herein, in the first place, classic network regulation operates, e.g., the control of the regulable network transformers. If the network operator cannot protect his network without the assistance of controllable components of the low voltage network, e.g., smart buildings, there must be a “priority signal” that is compulsory and to which the reaction is instantaneous.
A possibility for implementing the priority signal is the known audio-frequency ripple control system, TRA. With this, loads such as storage heaters are controlled by a control center. Herein, however, there are technical problems, by reason of which the TRA is relieved increasingly by other devices by network operators. Smart meters represent, in part, the successors that can either themselves, or via an additional gateway, switch individual components. It is therefore already technically possible to transmit a unidirectional ON/OFF command. If a plurality of components receive such a command simultaneously, through the simultaneous switching of the collective loads, problems can arise that can be lessened by a grouping of loads (e.g. per substation) and a temporally offset transmission of the switch-off commands, which occurs centrally from the control center.
However, these methods of unidirectional transmission of control commands for use as a priority signal are too global and too coarse for the targeted protection of selected low voltage networks.